contributes to male assertiveness and agressiveness (this is more of a stereotype and has been dismissed by researchers as over-simplification)

after birth (usually at puberty) contributes to the deepening of the voice, growth of the beard and auxilary hair

Fitness & Bodybuilding Relevance.

In terms of fitness, it's easy to understand why females have to work much harder at the gym to achieve results because without sufficient testosterone levels it is difficult to tone, increase muscle mass or decrease fat.

For males who exercise, they are able to achieve muscle gains and fat loss fairly quickly compared to their female counterparts.

Testosterone is also the natural enemy of fat. The more muscle mass an individual has the more it will promote fat burning.

Think about the areas on the body where fat tends to accumulate. Fat never forms around the biggest muscles on the body such as the back, quadriceps or chest (for males). It accumulates around the areas where our body has the thinnest muscles: abdominal and oblique area, hips, neck and butt.

Of course it's important to note that men and women will tend to accumulate fat in different areas of the body.

Thus, for serious athletes and bodybuilders it is essential to maintain high testosterone levels through natural testosterone enhancing supplements and estrogen blockers.

In addition to exercise and taking supplements, the decline in testosterone levels over time can be mitigated by a proper diet and healthy lifestyle. It's important to note that the decline in testosterone levels cannot be stopped altogether, it can only be slowed down by implementing the methods mentioned above.